Multichannel sound reproduction systems, including amplifiers, cables, loudspeakers and room acoustics, will always affect the spectral, transient and spatial properties of the reproduced sound, typically in unwanted ways. Whereas the technical quality of the components, such as amplifiers and loudspeakers, can generally be assumed to be high nowadays, sound reproduction nevertheless suffers from sound quality degradation for multiple reasons. Some of them will be discussed in the following.
First, the acoustic reverberation of the room where the equipment is placed has a considerable and often detrimental effect on the perceived audio quality of the system. The effect of reverberation is often described differently depending on which frequency region is considered. At low frequencies, reverberation is often described in terms of resonances, standing waves, or so-called room modes, which affect the reproduced sound by introducing strong peaks and deep nulls at distinct frequencies in the low end of the spectrum. At higher frequencies, reverberation is generally thought of as reflections arriving at the listener's ears some time after the direct sound from the loudspeaker itself. Reverberation at high frequencies cannot be generally assumed to have a detrimental effect on sound quality. Nevertheless, reverberation definitely has an effect on timbral and spatial sound reproduction.
Second, established loudspeaker-based multichannel sound reproduction standards, such as stereo or 5.1 surround (e.g., home cinema systems), generally assume a symmetric setup of the sound system. It is assumed that multichannel signals, which are in some way coded in the recording, are reproduced via loudspeakers that are placed at defined angles and distances from the listener. Such a symmetric setup is usually found in, for example, professional recording studios. In reality however, such a symmetrical setup is unrealistic when considering typical listening environments such as consumer homes. In these environments, other factors such as the furniture, determine the location of the loudspeakers and listener, rather than placing them with regard to the suggestion in the standards. This leads to impaired sound reproduction and consequently detrimental sound quality.
Third, these multichannel standards generally assume one listener, which is located in a certain position, often referred to as sweet spot. This sweet spot is typically rather small and corresponds to a limited region in space. Yet, high fidelity sound reproduction, that is sound reproduction with a high amount of accuracy and trueness with respect to the recording, is only provided in the sweet spot. Outside this limited region, sound reproduction is severely deteriorated. This also yields impaired sound quality for one or several listeners, which are located outside the given sweet spot.
Last, sound reproduction by means of multiple loudspeakers always has a conceptual problem of identity. Exact reproduction of recorded sound by means of multiple loudspeakers in other than the genuine recording environment must be considered an impossible task. This is particularly valid for the spatial aspects of multichannel sound reproduction, which will always correspond to an approximation of the recorded sound field rather than true (high fidelity) reproduction of it. Therefore, sound quality also depends on human expectation and experience with regard to the presented multichannel method. Whereas sound reproduction may not be accurate in many cases, it may still be plausible to the listener, and thus perceived as proper spatial sound reproduction. Therefore, the fidelity of sound reproduction can generally be improved relative to a given listening situation.